Major donors are shutting the money spigot to Mayor de Blasio’s re-election campaign as corruption probes swirl around City Hall, according to sources and campaign filings.

De Blasio, the subject of state and federal investigations into his fundraising, collected 19 percent less cash in the second half of 2016 compared to the first half. From July to December, he collected $842,728 from 2,788 donors. In the six months prior, he cashed $1.04 million from 1,216 donors, according to city campaign finance records.

Much of the drop in campaign cash is due to the wealthiest donors shunning Hizzoner as the probes heated up. The number of individuals who give the maximum allowed by law — $4,950 per primary and general election — plummeted from 130 to only 87.

And the total amount those “max donors” contributed nosedived from $633,600 in the first half of last year to $391,050 in the second half.

Even de Blasio’s biggest bundlers have abandoned ship.

“I don’t think I would give money right now,” one top fundraiser told The Post. “None of my clients will give money right now. I don’t know any industry that would. Nobody wants to get calls from the feds.”

‘None of my clients will give money right now. … Nobody wants to get calls from the feds.’

“He’s trying to raise the max from donors and he’s having trouble,” said another benefactor who maxed out despite de Blasio’s troubles. “The coverage of him going to meet with people in the U.S. attorney’s office has been harmful. People want to see how it plays out.”

No one has come forward to challenge the mayor in the Democratic primary, but little-known Republican Paul Massey has pulled in $1.6 million in just six months for the November election. De Blasio has $3.3 million in his coffers, amassed over three years.

De Blasio has continued to hold fundraisers, but his outreach to top donors in the real estate, finance, and political worlds has been muted, multiple sources said.